Enhanced multilevel memory

1. A method comprising: storing states in one or more multilevel memory cells, said storing states comprising encoding said states according to a convolutional code to provide symbols representing said states; and determining said encoded states using soft decision and convolutional decoding, wherein determining further comprises: reading soft decisions associated with sensed threshold voltages from the multilevel memory cells; maintaining sets of periodic functions, wherein each set is associated with a different plurality of program distributions of stored states, wherein the stored states associated with a particular periodic function are periodic with respect to one another; associating a soft decision with a particular set of the periodic functions; and selecting a program distribution from the particular set of periodic functions based at least partly on a calculation of a most probable encoding path that had been followed for encoding.

2. The method of claim 1 , wherein said determining said encoded states further comprises: retrieving said stored states from said stored values and applying said soft decision and convolutional decoding to recover said stored states.

3. The method of claim 1 , wherein said soft decision comprises determining a most probable program state among a plurality of program states to determine said encoded states.

4. The method of claim 1 , wherein said multilevel memory cells are capable of storing two or more bits.

5. The method of claim 1 , wherein said values comprise a measurement of a probability that a sensed threshold voltage belongs to a particular program distribution of said one or more multilevel memory cells.

6. A memory device comprising: a memory array to store states across one or more multilevel memory cells; and a controller configured to: encode said states according to a convolutional code to provide symbols representing said states; read soft decisions associated with sensed threshold voltages from the multilevel memory cells; access sets of periodic functions, wherein each set is associated with a different plurality of program distributions of stored states, wherein the stored states associated with a particular periodic function are periodic with respect to one another; associate a soft decision with a particular set of the periodic functions; and select a program distribution from the particular set of periodic functions based at least partly on a calculation of a most probable encoding path that had been followed for encoding to determine said encoded states using soft decision and convolutional decoding.

7. The memory device of claim 6 , wherein said soft decision comprises determining a most probable program state among a plurality of program states to determine said encoded states.

8. The memory device of claim 6 , further comprising: a sensing circuit to determine said threshold voltages of said one or more multilevel memory cells; and a converter to convert said values to a digital sequence of numbers indicating said threshold voltages of said one or more multilevel memory cells.

9. The memory device of claim 8 , wherein said sensing circuit comprises a voltage comparator having multiple inputs to receive a bit line voltage corresponding to one of said one or more multilevel memory cells and a reference voltage.

10. The memory device of claim 6 , wherein said multilevel memory cells are capable of storing two or more bits.

11. The memory device of claim 6 , further comprising: a decoding unit to generate said values to quantify a probability that a sensed threshold voltage belongs to a particular program distribution of said one or more multilevel memory cells.

12. A system comprising: a memory device comprising: a memory array configured to store states across one or more multilevel memory cells, and a controller configured to: encode said states according to a convolutional code to provide symbols representing said states; read soft decisions associated with sensed threshold voltages from the multilevel memory cells; access sets of periodic functions, wherein each set is associated with a different plurality of program distributions of stored states, wherein the stored states associated with a particular periodic function are periodic with respect to one another; associate a soft decision with a particular set of the periodic functions; and select a program distribution from the particular set of periodic functions based at least partly on a calculation of a most probable encoding path that had been followed for encoding to determine said stored states using soft decision and convolutional decoding; and a processor to host one or more applications and to initiate write and/or read commands to said memory device controller to provide access to said memory array.

13. The system of claim 12 , wherein said soft decision comprises determining a most probable program state among a plurality of program states to determine said stored states.

14. The system of claim 12 , further comprising: a sensing circuit to determine said threshold voltages of said one or more multilevel memory cells; and a converter to convert said values to a digital sequence of numbers indicating said threshold voltages of said one or more multilevel memory cells.

15. The system of claim 14 , wherein said sensing circuit comprises a voltage comparator having multiple inputs to receive a bit line voltage corresponding to one of said one or more multilevel memory cells and a reference voltage.

16. The system of claim 12 , wherein said convolutional encoding comprises Viterbi encoding.

17. The system of claim 12 , further comprising: a decoding unit to generate said values to quantify a probability that a sensed threshold voltage belongs to a particular program distribution of said one or more multilevel memory cells.

18. The method of claim 1 , further comprising storing said values as multi-bit strings in said one or more multilevel memory cells.

19. The method of claim 18 , wherein said storing said values as multibit strings in said one or more multilevel memory cells further comprises storing said values as multi-bit strings in two or more of said multilevel memory cells.

20. The memory device of claim 6 , wherein said controller is further adapted to store said values as multi-bit strings in said one or more multilevel memory cells.

21. The method of claim 1 , wherein the sets of periodic functions are maintained in a lookup table.

22. The memory device of claim 6 , further comprising a look-up table configured to store the sets of periodic functions.

23. The system of claim 12 , further comprising a look-up table configured to store the sets of periodic functions.